Overload protective system



April 8 1924".

' OVERLOAD PROTECTIVE SYSTEM Filed April 26 1922 Patented Apr. 8, 1924.

UNITED STATES FELIX TOBIEN, 0F ESSEN, GERMANY,

ASSIGNOR- TO FRIED. KRUPP AKTIE'N- GESELLSCHAFT, 0F ESSEN-ON-THE-RUHR, GERMANY.

OVERLOAD I"IROTECTIVE SYSTEM.

Application filed April 26, 1922. Serial No. 556,718.

To all whom it may concern:

Be it ltnown that I, FELIX ToinnN, residing' at Essen. Germany. a citizen of the German Republic. have invented a certain new and useful Improvement in Overload Protective Systems. of which the following is a specification.

This invention relates to improvements in overload protective systems for motors which are started by means of a starting resistance.

The invention has for its object to provide an overload protective system of the character stated in which the sensibility of the protective device is made dependent on the starting operation in. such a manner that the electric system possesses the lowest sensibility at the beginning of the starting andthe highest sensibility at the end of the starting, the sensibility gradually increasing during the starting operation.

According; to the invention, this object is attained by subjecting the magnetic circuit of an overload circuit-breaker comprising a main current releasing coil and a holding coil, to the influence of an exciting current the strength of which is always dependent on the resistance value of the cutin portion of the starting resistance.

In the drawing, two embodiments of the subject matter of the invention are diagrammatically illustrated, Fig. 1 being the first and Fig. 2 the second embodiment.

Referring now to the drawing. the first embodiment will be described first. Placed in the main current line in series with the armature B of a main current motor B B which is connected to a source of direct current, are a starter D D on the one hand. and on the other hand the break formed by contact members E and E which are movable with relation to each other, and the main current releasing coil E of an overload circuit-breaker. One, E of these contact members is under the action of a spring E which tends to hold the circuit-breaker in its closed position while the other contacts, E, are fixed. The overload circuitbreaker further possesses another exciting winding E which is constructed as a high resistance coil and which, together with a series resistance F, is connected in parallel to the section of the main current circuit containing the releasing coil E and the contact members E E of the overload circuitbreaker, and which is wound in the same sense as the releasing coil E This second exciting winding E which serves to hold the opened overload circuit-breaker in its open position, will hereinafter be called holding coil. A third magnet coil E of the overload circuit-breaker is connected to the terminals of the startin resistance D in such manner that. during the starting operation, a current will flow through it in the direction of the arrow 10. As this current is directed oppositely to the currents passing through the coils E and E in the direction of the arrows y and z in the operation of the overload, circuit-breaker, the additional magnet coil R will exert an action weakenin the ma gnetic pulling force of the two other magnetic coils. This action will be strongest when the entire starting resistance l) is cut in. and it will decrease the more. the more the portion of the starting resistance D, through which the motor current passes. is reduced in the course of the starting operation by moving the starting lever D in the direction of the arrow :11.

In order to start the motor B B, the starting lever D is rotated in the direction of the arrow 00. As soon as the lever will come into contact with the starting resistance D, the magnet winding B and the armature B of the motor B B will receive a current oi. moderate strength; the currents passing through the coils E and E in the direction. of the arrows g and z, are at first likewise of low strength only, because of the starting resistance 1) being cutin. However. the third coil E, which weakens the action of the two other magnet coils. is fully excited. According as the starting lever D is moved on, the strength of current in. the main current releasing coil E of the overload circuit-breaker will rise, while it will lower in the counter coil E, so that the motor armature B will start rotating and the sensibility of the overload circuit-breaker with respect to overload will increase the more, the more the motor armature B will approach to its working number of revolutions and. accordingly. to its normal rate of operation. During the starting operation, the overload circuit-breaker will therefore only enter into action at a considerably higher overload than after the starting operation has been terminated, when its magnetic pulling force will considerahlv increase hecause of the stopping of the oount i action o the con E.

of current in the holding coil E under the influence of the rapldly he oisturbing cause has been obviclrcuit-ln'ealqer can again he closed or 1 n the St-1ilil1lfi lever D hacl; until it rests no longzer on the starting 1' sis'ance D. The main line containing the motor B Will thus he interrupted so that the holding coil E will likewise bccon'te curcircuit-brealzer will I, in which, with an overload circuii-hrea *er alrcar present, an in rease of the magnetic pulling force hcvont "the value detern'iined liv the Inain current releasing coil does not come into question, i i ch it is found desirable to re luce e'ic pulling force during the ti rti operation for the purpose of reduc 1e sensibility or" the overload circuit- ,realrer.

In opposition to the system according to Fig". 1 the electric connections of the overload CllClllt-bluillIQl' in the second einhodinient ot the invention illustrated in Fig. 2 are so that the current coming from the positive pole of the source of current will lirst pass through the hreal: E and the series resistance l and only thereafter through the main current releasingcoil E and the holding coil E Besides, the starter D D is placed between the overload circ:iit-hreake' and the motor lil B illlCl is a direct current motor. The open end ot the starting resistance D is connected h a conductor G containing a resistance to the point of connection between the oldiuo' coil and the series resistance F. The strength of the current passing: during ti o starting operation through the holding coil ii in the direction of the arrow 2, which is opposite to the direction of the current in the releasing coil E (arrow 1 will therefore depend on the voltage drop caused in the starting resistance D by the rurrcnt passing through the same. This volteuc drop will he largest when the start-- ing lerer l)" touches the free end of the resistance D; it will become equal to zero when the lever D moved in the the arrow .r. will reach the the starting re tines, and the 1 ol the starting resi nce l) put in circuit l kewise equal to mlding coil E will therefore call'euiug action on the ll'lll t flltti l w o i the overload circuit-hrcalier sterling operation. this J'Qllh'ttllr r at the hcginnin 11 starting operation and siiuillest a o same. il heirtoia the opshoivu in 111g. 2 is o that of the Qllllllfllll'iltllt acllowcrcr, the system a r-gscsscs over the fir t advantage that no addiivinding" hut onl a further a motor c ntrol system, a motor a sarting rheostat, an overload havingcontacts in said circuit. a

on said swit h in said inotor cir- \Jllltllng causing said switch to energized above a certain value, ling to close said switch. a cirin parallel to said Winding contacts and comprising a ding of said switch, said second Winding. when energized, preventing switch trorn closing under the action I"; .1 spring, and a circuit connected in l to said starting rheostat, said circoinprising Winding on said switch, inc-ling. when cner ize 'l. counteracts uned switch \vindinc thereby acthe sensibility of said sivitoh 2 in electric overload protective system,

a nialn current circuit. a nnaor, lance tor the motor and an circuit-breaker consisting of a main current releasing coil and g coil, the starting resistance being act-Ween the armature oil the motor is switch of the overload circuitholdingr coil being a rranged the break of the overload ciras to the starting rea starting ref ove load sen, h-erniany this 28th day of March, 1922.

FELIX TOBIEN. 

